The invention pertains to interconnectable ambient condition detectors. More particularly, the invention pertains to such detectors which include low power, local alarm indicating circuits.
Interconnected smoke detector systems are known. In such systems, a plurality of spaced apart smoke detectors, installed in a region being monitored, are interconnected by conductors. When one detector goes into alarm, it emits an interconnect alarm signal, via the conductors, to the remaining detectors. In this configuration, all of the remaining detectors also go into a remote alarm. The system stays in alarm until the smoke clears and/or the system is reset.
A long term problem has been establishing the detector(s) which have gone into local alarm after the alarm condition has cleared. A faulty detector which has gone into a false alarm will drive all of the remaining detectors to emit an interconnect alarm. In such circumstances, knowing which detector went into local alarm will facilitate the identification and replacement of the faulty unit.
One known solution has been to blink a local light emitting diode on each detector which has gone into a local alarm for the duration of that alarm condition. The blinking ceased however when the respective detector(s) would go out of local alarm. Hence, there would be no after-the-fact record available as to the detector(s) that went into local alarm.
Another known solution has been to provide a two-state device such as an SCR or triac which would conduct in the presence of a local alarm and light an indicator such as a light emitting diode. A gate signal for the SCR or triac has been generated using a signal that activates a local audible output transducer.
Use of an SCR or triac produces an after-the-fact indicator of the presence of a local alarm condition. In such known systems, where an interconnect signal is received before the respective detector goes into local alarm, the interconnect signal is used to inhibit the gate signal. Hence, only the indicator for the first to alarm detector will be energized.
Use of the SCR or triac-type latch turns the indicator on continuously. This represents a power drain that requires a source of AC input power. Hence, such configurations are not suitable for use in battery powered detectors due to high current drain.
There thus continues to be a need for latching circuitry which can indicate, over an extended period of time if need be, which detector(s) in an interconnected system has or have gone into local alarm. Preferably, such circuitry could be configured to require minimal power consumption so that the respective units can be energized off of batteries without requiring the presence of AC-type utility power.
An interconnectable detector includes a relatively low powered latch circuit which responds to an output signal from a local ambient condition sensor. The latch is set each time that the sensor indicates the presence of a hazardous condition such as fire or gas. This corresponds to a local alarm condition.
The sensor and the latch circuitry are carried within a housing. The housing, in one aspect of the invention, also carries an externally viewable light emitting indicator, such as a light emitting diode. A control circuit couples the sensor to the latch circuitry and to the visual output device.
In yet another aspect of the invention, the housing also carries an interconnect port. The interconnect port transmits alarm indicating signals to other detectors coupled to an intervening communication link, for example, wirelessly or via a wire cable. In response to a first detector going into an alarm condition, and as a result setting its local alarm latch, an interconnect alarm signal is generated. The interconnect alarm signal is transmitted to the remaining detectors coupled to the communication link. Those detectors go into an interconnect alarm. They do not set their respective local alarm latches. This corresponds to a remote or an interconnect alarm.
The latch circuitry is configured such that where a local alarm condition is sensed, that detector""s respective alarm latch will be set irrespective of the presence of the interconnect alarm signal. Subsequently, after the system has gone out of alarm due to the alarm causing condition having dissipated, the respective alarm latches which had been set due to detection of the local respective alarm condition remain set.
The state of the respective alarm latch can be interrogated by activating a test switch associated with each detector. Activating the test switch, for example by depressing same, of a detector which has an alarm latch which has been set will result in the local visual indicator being energized so as to indicate, for a period of time such as 10 minutes, for example, that a particular detector had previously gone into a local alarm. At the same time, the respective detector emits an interconnect alarm signal, due to activation of the test switch.
The emitted interconnect alarm signal in turn causes all of the interconnected detectors to go into an interconnect (remote) alarm state for as long as the initial test switch has been activated. When the test switch is de-activated, such as by releasing same, the interconnected detectors go out of alarm. At the same time, any of the interconnected detectors which had their respective alarm latches set will at that time energize their alarm indicator for a pre-set time interval to indicate that those respective detectors had at some prior time gone into a local alarm.
In another aspect of the invention, the visual indicator can be energized intermittently so as to flash rapidly, for example, at a rate of once every one to two seconds for the pre-determined time interval, such as for ten minutes, and then stop. In yet another aspect of the invention, releasing the respective test switch will re-set the associated local alarm latch. Alternately, the local alarm latch can be reset at the end of the ten-minute interval. Also, the alarm latch can be reset, in another embodiment, by activating the test switch a second time.
In yet another aspect of the invention, alarm latches can be implemented as, for example, bi-stable multi-vibrator circuits which exhibit the same energy requirements irrespective of state. As a result of using relatively low power circuitry and blinking the visual output element, a battery can be used as a source of energy.
In another aspect of the invention, the sensor can be implemented as a smoke sensor, a heat sensor or a gas sensor. Smoke sensors can be implemented as either ionization or photoelectric smoke sensors.
The detector can incorporate alarm silencing circuitry for purposes of terminating nuisance alarms. In addition, activation of the test switch will produce a condition for testing portions of the respective detector for as long as the test switch is activated. The test switch can be activated locally, by depressing it, or remotely by a wireless command.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.